Rolled Copper Foil and Manufacturing Method of Rolled Copper Foil

ABSTRACT

A rolled copper foil, according to the present invention, obtained after a final cold rolling step but before recrystallization annealing includes a group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction (XRD) pole figure measurement with respect to a rolled surface. In the XRD pole figure measurement, at least four peaks of a {220} Cu  plane diffraction of a copper crystal due to the group of crystal grains exhibiting the four-fold symmetry, which is obtained during β axis scanning with an α angle set to 45°, appear at intervals of 90°±5° along the β angle.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent application serial no. 2008-112476 filed on Apr. 23, 2008, which further claims priority from Japanese patent application serial no. 2008-001069 filed on Jan. 8, 2008, the contents of which are hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a rolled copper foil and, particularly, it relates to a rolled copper foil which has an excellent flexible fatigue property suitable for flexible wiring materials such as flexible printed circuits.

2. Description of Related Art

Flexible printed circuit (hereinafter simply referred to as FPC) boards have high freedom in a mounting form to electronic equipment due to their attractive features of small thickness and excellent flexibility. Accordingly, FPC boards have been used generally as, e.g., wirings for bending portions of foldable (clamshell type) cellular phones, movable portions of digital cameras, printer heads, etc., and movable portions of equipment relevant to disks such as HDDs (hard disk drives), DVDs (digital versatile disks) and CDs (compact disks).

As conductors for FPC board, pure copper foils or copper alloy foils (hereinafter collectively referred to as the copper foils) with various types of surface treatment applied have been generally used. The copper foils are classified into electrodeposited copper foils and rolled copper foils according to the manufacturing methods thereof. Since FPC boards are used as wiring materials for repetitively moving portions as described above, an excellent flexible fatigue property (e.g., flexible fatigue property of 1,000,000 cycles or more) has been required, and rolled copper foils are often selected as the copper foils.

Generally, the rolled copper foils are manufactured by applying a hot rolling step to a cast ingot made of tough pitch copper (JIS H3100 C1100) or oxygen-free copper (JIS H3100 C1020) as a raw material, and then by repeating a cold rolling step and a process annealing step until a predetermined thickness is proved. The thickness of rolled copper foils required for FPC boards is usually 50 μm or less, and in recent years thinner foils for FPC boards have been demanded to ten-odd μm or less.

A manufacturing for the FPC board generally comprises: “a step of bonding a copper foil for an FPC board and a base film (base material) comprising resin such as polyimide to form a CCL (copper clad laminate) (CCL step)”; “a step of forming a printed circuit by a method such as etching for the CCL”; “a step of applying surface treatment on the circuit for protection of the wirings”, etc. The CCL step includes two kinds of methods, i.e., a method of laminating a copper foil and a base material with an adhesive and then curing and adhering the adhesive by heat treatment (3-layered CCL), and a method of directly bonding a copper foil to which surface treatment has been applied to a base material without an adhesive and then integrating them by heating and pressing (2-layered CCL).

In the FPC board manufacturing step, cold rolled copper foils (in a hard state in which they are work hardened) have been often used from a viewpoint of easy handling. In a case where the copper foil is in an annealed (softened) state, the copper foil is easy to deform (e.g., elongation, creasing, flexing, etc.) upon cutting of the copper foil or lamination with the base material, resulting in a product failure.

On the other hand, the flexible fatigue property of the copper foil is improved remarkably by applying recrystallization annealing, as compared with the copper foil in the as-rolled state. Then, a manufacturing method has been generally selected in which the heat treatment for adhering the base material and the copper foil in the CCL step is also served for recrystallization annealing for the copper foil. The heat treatment condition in this case is usually at a temperature of 180° C. to 300° C. for 1 to 60 minutes (typically at 200° C. for 30 minutes) and the copper foil is in a state refined into a recrystallization texture.

For improving the flexible fatigue property of FPC boards, it is effective to improve the flexible fatigue property of the rolled copper foil as the material thereof. Further, it has been known that the flexible fatigue property of the copper foil after recrystallization annealing is more improved as a cubic texture is developed. In general, “development of the cubic texture” only means that the occupation ratio of a {200}_(Cu) plane is high at the rolled surface (e.g., 85% or more).

Heretofore, for rolled copper foils with an excellent flexible fatigue property and rolled copper foil manufacturing methods, there have been reported as follows. They are: e.g., a method of developing the cubic texture by increasing a total working ratio in a final cold rolling step (to, e.g., 90% or more); a copper foil defined for the degree of development of the cubic texture after recrystallization annealing (e.g., the intensity of a (200)_(Cu) plane determined by X-ray diffraction to the rolled surface is at least 20 times greater than that of the (200)_(Cu) plane determined by powder X-ray diffractometry); a method of further developing the cubic texture after recrystallization by developing the cubic texture during process annealing before the final cold rolling step to increase the total working ratio in the final cold rolling step to 93% or more; a copper foil for which the ratio of penetration crystal grains in the direction of thickness of the copper foil is defined (e.g., 40% or more as a cross sectional area ratio); a copper foil for which the softening temperature is controlled by the addition of a small amount of additive elements (e.g., controlled to a half-softening temperature of 120 to 150° C.); a copper foil for which the length of a twin boundary is defined (e.g., the total length of the twin boundary with a length exceeding 5 μm in an area of one square millimeter is 20 mm or less); a copper foil for which the recrystallization texture is controlled by the addition of a small amount of additive elements (e.g., the Sn is added by 0.01 to 0.2 mass % to control the average crystal grain size to 5 μm or less and the maximum crystal grain size to 15 μm or less), etc. (see, e.g., JP-A-2001-262296, JP-B-3009383, JP-A-2001-323354, JP-A-2006-117977, JP-A-2000-212661, JP-A-2000-256765, and JP-A-2005-68484).

As described above, it is reported that, in the prior art, as the total working ratio is increased, the cubic texture of the rolled copper foil is developed after recrystallization annealing and thereby the flexible fatigue property is improved. In cold rolling working, however, as the final rolling working ratio increases, the material (copper foil) becomes harder due to work hardening. It then becomes difficult to control the working ratio per rolling pass, lowering the efficiency of copper foil manufacturing. Specifically, when the total working ratio reaches about 90% (particularly, 93% or more), control of the working ratio per rolling pass and rolling itself become rapidly difficult.

In recent years, however, along with development in downsizing of electronic equipments, an increase in their integration degree (higher density mounting), and their higher performance, requirements for more improved flexible fatigue property than before have been increasingly made for FPC boards. Since the flexible fatigue property of the FPC board is determined substantially depending on that of the copper foil, it is essential to further improve the flexible fatigue property of the copper foil so as to satisfy the requirements. More and more demands for low costs of electronic components also rise.

SUMMARY OF THE INVENTION

Under these circumstances, it is an objective of the present invention to provide a rolled copper foil which is suitable to flexible wiring materials such as for flexible printed circuit (FPC) boards and has an excellent flexible fatigue property. Furthermore, it is another objective of the present invention to provide a method of stably manufacturing a rolled copper foil with an improved flexible fatigue property in an efficient manner (i.e., at a low cost) without carrying out working at a high degree, as is done in the prior art, in the final cold rolling step.

As the results of detailed metal crystallographic studies on a rolled copper foil by the inventors, it was found that there was a specific correlation among: the crystal grains orientation of a rolled copper foil after green sheet annealing and before the final cold rolling step; that of the rolled copper foil after the final cold rolling step and before the recrystallization annealing; that of the rolled copper foil after the recrystallization annealing; and the flexible fatigue property of the copper foil. It was also found that this correlation seems to be different from the principle that has been considered. Based on these findings, the present invention has been completed as described below. (Details will be described later.)

(1) According to one aspect of the present invention, a rolled copper foil obtained after a final cold rolling step but before recrystallization annealing includes a group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction pole figure measurement with respect to a rolled surface, in which at least four peaks of a {200}_(Cu) plane diffraction of a copper crystal due to the group of crystal grains exhibiting the four-fold symmetry, which is obtained by β axis scanning with an α angle set to 45°, appear at intervals of 90°±5° along the β angle.

Besides, as a material for the rolled copper foil, is preferably used a copper metal with a purity of 99.9% or more (so-called three nines up) such as a tough pitch copper (e.g., JIS H3100 C1100), an oxygen-free copper (e.g., JIS H3100 C1020) and etc. Furthermore, a copper alloy with the copper purity of 99.9% or more may be also used.

In the above aspect (1), the following modifications and changes can be made.

(i) The diffraction peaks exhibiting the four-fold symmetry at intervals of 90°±5° along the β angle each have a diffraction intensity at least 1.5 times stronger than a minimum intensity of {200}_(Cu) plane diffractions of the copper crystal, which are obtained by the β axis scanning.

(ii) When normalized intensity of the {200}_(Cu) plane diffractions of the copper crystal in results obtained by the X-ray diffraction pole figure measurement with respect to the rolled surface by the β axis scanning at respective α angles are plotted on a vertical axis with the α angle on a horizontal axis, the maximum value β of the normalized intensity appears in a range of the α angle from 25° to 35°; the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°; the normalized intensity increases monotonically in the range of the α angle from 85° to 90°; and the maximum value P, the maximum value Q, and the normalized intensity R at an α angle of 90° have a relation of “Q≦P≦R”.

(iii) In results obtained by X-ray diffraction 2θ/θ measurement for the rolled surface, diffraction peak intensity of a {200}_(Cu) plane of the copper crystal is equal to or greater than that of the {220}_(Cu) plane of the copper crystal.

(iv) The rolled copper foil further includes another group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction pole figure measurement with respect to the rolled surface; and at intervals of 90°±10° along the β angle appear the {220}_(Cu) plane diffraction peaks due to the another group of crystal grains exhibiting the four-fold symmetry, which are obtained by the β axis scanning within the range of 40° to 50° of the α angle.

(2) According to another aspect of the present invention, a rolled copper foil to which a recrystallization annealing is applied after a final cold rolling step has a relation of “[A]×[B]×[C]≧0.5”, where [A] is a cubic texture ratio calculated from results by X-ray diffraction 2θ/θ measurement carried out for a rolled surface, [B] is an out-of-plane alignment ratio calculated from results by X-ray diffraction rocking curve measurement carried out for a crystal grain with the cubic texture, and [C] is an in-plane orientation ratio calculated from results by X-ray diffraction pole figure measurement carried out for the crystal grain with respect to the rolled surface.

(3) According to another aspect of the present invention, a manufacturing method of a rolled copper foil, in which the rolled copper foil obtained after a final cold rolling step but before recrystallization annealing includes a group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction (XRD) pole figure measurement with respect to a rolled surface. In the XRD pole figure measurement, at least four peaks of a {220}_(Cu) plane diffraction of a copper crystal due to the group of crystal grains exhibiting the four-fold symmetry, which is obtained by β axis scanning with an α angle set to 45°, appear at intervals of 90°±5° along the β angle. In the manufacturing method of the rolled copper foil, one or more rolling passes in a second rolling pass and later in the final cold rolling step have a working ratio at least 1.1 times greater than an immediately preceding rolling pass.

In the above aspect (3), the following modifications and changes can be made.

(iv) A final pass or a pass immediately before the final pass in the final cold rolling step has the largest working ratio per pass though the second rolling pass and later.

(v) A total working ratio in the final cold rolling step is 80% or more and less than 90%.

(4) According to another aspect of the present invention, a manufacturing method of a rolled copper foil, in which the rolled copper foil obtained after a final cold rolling step but before recrystallization annealing includes a group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction (XRD) pole figure measurement with respect to a rolled surface. In the XRD pole figure measurement, at least four peaks of a {220}_(Cu) plane diffraction of a copper crystal due to the group of crystal grains exhibiting the four-fold symmetry, which is obtained by β axis scanning with an α angle set to 45°, appear at intervals of 90°±5° along the β angle. Furthermore, when normalized intensity of the {220}_(Cu) plane diffractions of the copper crystal in results obtained by the XRD pole figure measurement with respect to the rolled surface by the β axis scanning at respective α angles are plotted on a vertical axis with the α angle on a horizontal axis, the maximum value P of the normalized intensity appears in the range of the α angle from 25° to 35°, the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°, the normalized intensity increases monotonically in the range of the α angle from 85° to 90°, and the maximum value P, the maximum value Q, and the normalized intensity R at the α angle of 90° have a relation of “Q≦P≦R”. And Moreover when, in results obtained by the XRD pole figure measurement by the β axis scanning at respective α angles with respect to the rolled surface of the rolled copper foil obtained after an annealing step for green sheet but before the final cold rolling step, the normalized intensity of the {220}_(Cu) plane diffractions of the copper crystal are plotted on the vertical axis with the α angle on the horizontal axis, the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°, the minimum value S of the normalized intensity appears in the range of the α angle from 20° to 40°, and the maximum value Q and the minimum value S have a relation of “2≦Q/S≦3”, this type of rolled copper foil being used as an annealed green sheet. In the manufacturing method of the rolled copper foil, a total working ratio in the final cold rolling step is 80% or more and less than 93%.

ADVANTAGES OF THE INVENTION

According to the present invention, it is possible to provide a rolled copper foil which is suitable to flexible wiring materials such as for flexible printed circuit boards and has an excellent flexible fatigue property. Furthermore, it is also possible to provide a method of stably manufacturing a rolled copper foil with an improved flexible fatigue property in an efficient manner (i.e., at a low cost).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration showing major crystal planes of a copper crystal related to the present invention.

FIG. 2 is a schematic illustration showing a relationship among an incident X-ray, detector, specimen, and scanning axes in an X-ray diffractometer.

FIG. 3 is an example of a diffraction pattern by X-ray diffraction 2θ/θ measurement carried out for a rolled surface of a rolled copper foil according to the present invention in a state after the final cold rolling step but before recrystallization annealing.

FIG. 4 is an example of a pole figure by X-ray diffraction pole figure measurement carried out for a rolled foil according to the present invention in a state after the final cold rolling step but before recrystallization annealing.

FIG. 5 schematically shows a relationship among a degree of crystal grains orientation, a full width at half maximum of an X-ray diffraction peak, and an integration width of the XRD peak.

FIG. 6 is an exemplary flowchart showing steps of manufacturing a rolled copper foil according to the present invention.

FIG. 7A is an example of a diffraction pattern of X-ray diffraction in-plane alignment measurement (measurement for a {220}_(Cu) plane with a set to 450) carried out for a rolled copper foil immediately after the final cold rolling step in Example 1; and FIG. 7B is another example of this measurement in Comparative example 1.

FIG. 8 is an example of a diffraction pattern by X-ray diffraction 2θ/θ measurement carried out for a rolled copper foil immediately after the final cold rolling step in Comparative example 1.

FIGS. 9A to 9D are examples of normalized intensity of {220}_(Cu) plane diffractions by β axis scanning as a function of α angle by X-ray diffraction pole figure measurement, which was carried out for rolled surfaces of annealed green sheets in Example 2, Example 3, Comparative example 2, and Comparative example 3, respectively.

FIGS. 10A to 10D are examples of normalized intensity of {220}_(Cu) plane diffractions by β axis scanning as a function of α angle by XRD pole figure measurement, which was carried out for rolled surfaces of rolled copper foils in way of the final cold rolling step in Example 2, Example 3, Comparative example 2, and Comparative example 3, respectively.

FIGS. 11A to 11D are examples of normalized intensity of {220}_(Cu) plane diffractions by β axis scanning as a function of α angle by XRD pole figure measurement, which was carried out for rolled surfaces of rolled copper foils immediately after the final cold rolling step in Example 2, Example 3, Comparative example 2, and Comparative example 3, respectively.

FIGS. 12A to 12C are examples of a diffraction pattern by XRD 2θ/θ measurement on rolled copper foils immediately after the final cold rolling step in Example 2, Example 3, and Comparative example 2, respectively.

FIG. 13 is a schematic illustration showing an outline of flexible fatigue property measurement (IPC-based fatigue test).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic illustration showing major crystal planes of a copper crystal related to the present invention. Since copper has a cubic crystal structure, the angle formed between a {200}_(cu) plane and a {220}_(Cu) plane is 45°. Herein, a pair of braces { } indicates an equivalent plane. (See FIG. 1.)

FIG. 2 is a schematic illustration showing a relationship among an incident X-ray, detector, specimen, and scanning axes in an X-ray diffractometer. “X-ray diffraction” is abbreviated to “XRD” in some portions in the description below. An evaluation (measurement) method for a state of the crystal grains alignment of a rolled copper foil through XRD is described below with reference to FIG. 2. The three scanning axes in FIG. 2 are generally referred to as a sample axis, which is the θ axis; a deflection axis, which is the α axis; and an in-plane rotation axis, which is the β axis. Further, the X-ray diffraction in the present invention is always carried out by using the Cu-Kα ray.

In XRD 2θ/θ measurement, the specimen and detector are scanned on the θ axis with respect to the incident X-ray, in which the scanning angles of the specimen and detector are θ and 2θ, respectively. According to intensity at a diffraction peak in the XRD 2θ/θ measurement, it can be evaluated which crystal plane is dominant at a specimen surface (rolled surface according to the present invention) of a polycrystalline rolled copper foil.

In XRD rocking curve measurement, only the specimen is scanned on the θ axis for the 20 value of a particular {h k l}_(Cu) diffraction plane (the scanning angle 2θ of the detector is fixed). According to the XRD rocking curve measurement, the degree of orientation of the {h k l}_(Cu) plane in a normal direction to the rolled surface can be evaluated by using full width at half maximum (FWHM_({hkl})) or integration width (IW_({hkl})) of the {h k l}_(Cu) plane diffraction peak. It can be said that the smaller the full width at half maximum or integration width the diffraction peak is, the more superior the crystal grains orientation in the normal direction to the rolled surface is. Herein, The crystal grains orientation perpendicular to the rolled surface is referred to below as the out-of-plane alignment. The full width at half maximum is defined as the width of a peak having intensity which is half the maximum intensity of the diffraction peak. The integration width is defined as a value obtained by dividing the integration intensity of a diffraction peak by the maximum intensity of the diffraction peak.

In XRD pole figure measurement, while a detector is fixed at the scanning angle of 2θ value of a certain plane {h k l}_(Cu), a specimen is scanned stepwise by the α-axis and is rotated in-plane (in-plane rotation of 0° to 360°) by the β-axis for each of α-values. In the XRD pole figure measurement of the present invention, the normal direction to the specimen surface is defined as α=90° to be a reference for the measurement. Further, while the pole figure measurement includes a reflection method (α=15° to 90°) and a transmission method (α=0° to 15°), only the reflection method (α=15° to 90°) of the pole figure measurement is conducted in this invention.

One of evaluation methods utilizing features of XRD pole figure measurement is in-plane alignment measurement. In this measurement, an angle formed between a particular {h k l}_(Cu) plane and a {h′ k′ l′}_(Cu) plane, which geometrically corresponds to the {h k l}_(Cu) plane, is assumed to be α′. α axis scanning is performed (a specimen is tilted) so that α becomes 90° minus α′ (α=90°−α′) for the 2θ value of the {h′ k′ l′}_(Cu) plane (with the scanning angle 2θ of the detector fixed), and then β axis scanning is performed for the specimen (in-plane rotation from 0° to 360°). According to the XRD in-plane alignment measurement, the degree of biaxial alignment of the {h k l}_(Cu) plane geometrically corresponding to the {h′ k′ l′}_(Cu) plane within the rolled surface can be evaluated by using the full width at half maximum (FWHM_({h′k′l′})) or the integration width (IW_({h═k′l′})) of the {h′ k′ l′}_(Cu) plane diffraction peak. It can be said that the smaller the full width at half maximum or integration width of the diffraction peak is, the more superior the crystal grains orientation in the in-plane direction of the rolled surface is, as described above (the crystal grains orientation within the rolled surface is referred to below as the in-plane alignment).

First Embodiment of the Present Invention

(In-Plane Alignment Measurement)

A rolled copper foil in this embodiment is the rolled copper foil after the final cold rolling step but before recrystallization annealing. In results obtained by the X-ray diffraction pole figure measurement with respect to the rolled surface, the rolled copper foil includes a group of crystal grains which exhibits four-fold symmetry, in which at least four peaks of a {220}_(Cu) plane diffraction of a copper crystal due to the group of crystal grains exhibiting the four-fold symmetry, which is obtained by β axis scanning with an α angle set to 45°, appear at intervals of 90°±5° along the β angle. For example, when the rolling direction of the copper foil is set to 0° of β angle in the pole figure measurement, centers of the four-fold symmetric peaks are approximately 0° (360°), 90°, 180°, and 270° of β angle.

If the {220}_(Cu) plane diffraction peaks do not exhibit four-fold symmetry at intervals of 90°±5° in the XRD in-plane alignment measurement, a rolled copper foil having an improved flexible fatigue property cannot be obtained even after recrystallization annealing. Accordingly, the above stipulation is made. Four-fold symmetry at intervals of 90°±5° of the {220}_(Cu) plane diffraction peaks, which are obtained by the β axis scanning with the α angle set to 45° in the XRD pole figure measurement, means that the {200 }_(Cu) plane which forms 450 with respect to the {220}_(Cu) plane from the viewpoint of the crystal geometry has an in-plane alignment at the rolled surface of the copper foil. Furthermore, it is desirable that the intensity of each of the four-fold symmetrical diffraction peaks be at least 1.5 times stronger than the minimum intensity of the {220}_(Cu) plane diffractions obtained by the β axis scanning (in-plane rotation from 0° to 360°).

Second Embodiment of the Present Invention

(Normalized Intensity)

A rolled copper foil in this embodiment is also the rolled copper foil after the final cold rolling step but before recrystallization annealing. When normalized intensity of the {220}_(Cu) plane diffractions of the copper crystal in results obtained by the XRD pole figure measurement with respect to the rolled surface by the β axis scanning at respective α angles are plotted on a vertical axis with the α angle on a horizontal axis, the maximum value P of the normalized intensity appears in a range of the α angle from 25° to 35°, the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°, the normalized intensity increases monotonically in the range of the α angle from 85° to 90°, and the maximum value P, the maximum value Q, and the normalized intensity R at the α angle of 90° have the relation of “Q≦P≦R”. If, in result obtained by the above XRD pole figure measurement, the normalized intensity of the {220}_(Cu) plane diffractions does not indicate the maximum value P in the range of the α angle from 25° to 35°, the maximum value Q in the range of the α angle from 40° to 50°, nor the monotonic increase in the range of the α angle from 85° to 90°; or the maximum value P, the maximum value Q, and the normalized intensity R at the α angle of 90° do not have the relation of “Q≦P≦R”, the rolled copper foil having an improved flexible fatigue property cannot be obtained even after recrystallization annealing. Accordingly, the above stipulation is made.

The normalized intensity R_(c) means a number of counts averaging a diffraction intensity of a predetermined {h k l}_(Cu) plane by the β axis scanning (in-plane rotation axis scanning) in the XRD pole figure measurement, the average diffraction intensity being calculated according to the following equation (refer to the following literature for details), as is disclosed in “RAD system, Application software, Texture analysis program handling manual (manual No. MJ201RE)” Rigaku Corp., pp. 22-23, and “CN9258E101, RINT 2000 Series, Application software, Pole figure program handling manual (Manual No. MJ10102A01)” Rigaku Corp., pp. 8-10.

Normalizing calculation is usually carried out using a computer.

R _(c) =I _(c) /I _(std)

where

I_(c): corrected intensity (background correction, absorption correction); and

I_(std): intensity for normalization determined by calculation.

The reason why normalized intensity is used is that specimens can be compared without being affected by a difference in condition settings such as a tube voltage or a tube current during the XRD pole figure measurement (apparatus dependence is essentially eliminated).

Third Embodiment of the Present Invention

(2θ/θ Measurement)

In results obtained by X-ray diffraction 2θ/θ measurement carried out for the rolled surface, a rolled copper foil after the final cold rolling step but before recrystallization annealing in this embodiment has a relation that diffraction peak intensity of the {200}_(Cu) plane is equal to or greater than that of the {220}_(Cu) plane (I_({200}Cu)≧I_({220}Cu)), where “I” means the intensity of a diffraction peak of the copper crystal.

As described before, when the rolled copper foil according to the present invention is in a state after the final cold rolling step has been applied and before recrystallization annealing is performed, the {200}_(Cu) plane is aligned at the rolled surface of the copper foil. This means that the rolled surface of the copper foil includes a significant amount of crystal grains oriented to the {200}_(Cu) plane. FIG. 3 is an example of a diffraction pattern by X-ray diffraction 2θ/θ measurement carried out for a rolled surface of the rolled copper foil according to the present invention in a state after the final cold rolling step but before recrystallization annealing.

As is clear from FIG. 3, the rolled surface has a strong diffraction intensity on the {200}_(Cu) plane and includes many crystal grains oriented to the {200}_(Cu) plane. If the rolled surface of the copper foil is not highly oriented to the {200}_(Cu) plane, the rolled copper foil having an improved flexible fatigue property cannot be obtained even after the recrystallization annealing. Accordingly, the above stipulation is made.

Fourth Embodiment of the Present Invention

(Pole Figure Measurement)

A rolled copper foil in this embodiment further includes another group of crystal grains which exhibits four-fold symmetry in addition to the one group of crystal grains exhibiting four-fold symmetry according to the first embodiment. In results obtained by X-ray diffraction pole figure measurement carried out for the rolled surface, the {220}_(Cu) plane diffraction peaks with the four-fold symmetry due to the another group of crystal grains appear at intervals of 90°±10° along the β angle, which are obtained by the β axis scanning within the range from 40° to 50° of the α angle.

For example, when the rolling direction of the copper foil is set to 0° of β angle in the pole figure measurement, centers of the four-fold symmetric peaks due to the another group of crystal grains are 45°±10°, 135°±10°, 225°±10°, and 315°±10° of β angle, in addition to those due to the one group of crystal grains observed at 0° (360°)±5°, 90°±5°, 180°±5°, and 270°±5° of β angle. Besides, “the another group of crystal grains exhibiting four-fold symmetry” in this embodiment may include a state in which at least three peaks among the four-fold symmetric {220}_(Cu) plane diffraction peaks (e.g., 45°±10°, 135°±10°, 225°±10°, and 315°±10° of β angle) are observed.

As mentioned before, four-fold symmetric peaks of the {220}_(Cu) plane diffraction, which are obtained by the β axis scanning within the range from 40° to 50° of the α angle in the XRD pole figure measurement, means that the {200}_(Cu) plane which forms 45° with respect to the {220}_(Cu) plane from the viewpoint of the crystal geometry has the in-plane alignment at the rolled surface (including an inclination of ±5° from the rolled surface) of the copper foil. Furthermore, the rolled copper foil including the another group of crystal grains exhibiting four-fold symmetry in addition to the one group of them according to the first embodiment leads that the rolled copper foil of this embodiment has more crystal grains well in-plane aligned at the rolled surface (seed crystal grains for a cubic texture described later) than that of the first embodiment, thereby improving the flexible fatigue property of the rolled copper foil.

FIG. 4 is an example of a pole figure by X-ray diffraction pole figure measurement carried out for a rolled foil according to the present invention in a state after the final cold rolling step but before recrystallization annealing. When the rolling direction of the copper foil was set to 0° of β angle, as shown in FIG. 4, four-fold symmetric diffraction peaks due to the another group of crystal grains (white-open arrows) were recognized within the range from 40° to 50° of the α angle in addition to those due to the one group of crystal grains (black arrows) according to the first embodiment. Such the rolled copper foil had a superior flexible fatigue property after the recrystallization annealing (details will be described later).

Fifth Embodiment of the Present Invention

(Overall Orientation Ratio)

A rolled copper foil in this embodiment is the rolled copper foil to which the recrystallization annealing is applied after the final cold rolling step. The rolled copper foil has a relation of “[A]×[B]×[C]≧0.5”, where [A] is a cubic texture ratio calculated from results by the XRD 2θ/θ measurement carried out for the rolled surface, [B] is a ratio of an out-of-plane alignment ratio calculated from results by the XRD rocking curve measurement carried out for a crystal grain with the cubic texture, and [C] is an in-plane alignment ratio calculated from results by the XRD pole figure measurement carried out for the crystal grain with respect to the rolled surface. In the present invention, “[A]×[B]×[C]” is defined as an overall orientation ratio. If the overall orientation ratio is less than 0.5 ([A]×[B]×[C]<0.5), an improved flexible fatigue property cannot be obtained. Therefore, the overall orientation ratio is set to 0.5 or more. It is preferably set to 0.55 or more and, more preferably, set to 0.6 or more.

Next, are described the cubic texture ratio [A], the out-of-plane alignment ratio [B] of the cubic texture, and the in-plane alignment ratio [C] of the cubic texture.

The cubic texture ratio [A] is defined as a value obtained by performing X-ray diffraction 2θ/θ measurement for a rolled surface of a rolled copper foil to which the recrystallization annealing is applied after the final cold rolling step, and then by calculating a ratio of the {200}_(Cu) plane diffraction peak which represents a cubic texture to all peaks from an equation described below.

Cubic texture ratio [A]=I _({200}Cu)/(I _({111}Cu) +I _({200}Cu) +I _({220}Cu) +I _({311}Cu))

where

I_({111}Cu): diffraction peak intensity of {111}_(Cu) plane;

I_({200}Cu): diffraction peak intensity of {200}_(Cu) plane, I_({220}Cu): diffraction peak intensity of {220}_(Cu) plane; and

I_({311}Cu): diffraction peak intensity of {311}_(Cu) plane.

The out-of-plane alignment ratio [B] of the cubic texture is defined as a value obtained by performing X-ray diffraction rocking curve measurement for the {200}_(Cu) plane of a rolled surface of a rolled copper foil to which the recrystallization annealing is applied after the final cold rolling step, and then by calculating a ratio of the full width at half maximum of the {200}_(Cu) plane diffraction peak to the integration width of the same peak from an equation described below.

Out-of-plane alignment ratio [B] of cubic texture=Δθ_(FWHM)/Δθ_(IW)

where:

Δθ_(FWHM): full width at half maximum of {200}_(Cu) plane diffraction peak; and

Δθ_(IW): integration width of {200}_(Cu) plane diffraction peak.

The in-plane alignment ratio [C] of the cubic texture is defined as a value by performing X-ray diffraction pole figure measurement for the {220}_(Cu) plane of a rolled copper foil with the α angle being 45° relative to the rolled surface, and then by calculating a ratio of full width at half maximum any one of four-fold symmetric {220}_(Cu) plane diffraction peaks obtained by the β axis scanning to integration width of the same peak from an equation described below.

In-plane alignment ratio [C] of cubic texture=Δβ_(FWHM)/Δβ_(IW)

where:

Δβ_(FWHM): full width at half maximum of {220}_(Cu) plane diffraction peak; and

Δβ_(IW): integration width of {220}_(Cu) plane diffraction peak.

Are explained below the reason why a ratio of the full width at half maximum of the diffraction peak to the integration width is taken to obtain the out-of-plane alignment ratio [B] and the in-plane alignment ratio [C]. FIG. 5 schematically shows a relationship among a degree of crystal grains orientation, the full width at half maximum of an X-ray diffraction peak, and the integration width of the XRD peak. When rocking curve measurement or in-plane alignment measurement is performed for a rolled copper foil with low crystal grains orientation, a diffraction peak shape, as shown in (a) in FIG. 5, that is relatively sharp near the center of its peak but has large tails is likely to be obtained. On the contrary, when rocking curve measurement or in-plane alignment measurement is performed for a rolled copper foil with high crystal grains orientation, a diffraction peak shape, as shown in (b) in FIG. 5, in which concentration occurs near the center of its peak is obtained.

Then, evaluating the full width at half maximum and integration width of these diffraction peaks, it is found that, in the case of (a) in which crystal grains orientation is low, there is a large difference between the full width at half maximum and the integration width, and that, in the case of (b) in which crystal grains orientation is high, the difference between the full width at half maximum and the integration width is very small. It can be considered that this distinction is caused by a difference in the size of the tails of the diffraction peak shape (a difference in the size of the tails in the diffraction peak shape). Accordingly, when a ratio of the full width at half maximum to the integration width of the diffraction peak is taken, the degree of crystal grains orientation of the rolled copper foil can be more clearly determined than when the full width at half maximum and integration width are individually compared.

[Manufacturing Method of Rolled Copper Foil]

Next, a manufacturing method of the rolled copper foil according to the present invention is described with reference to FIG. 6. FIG. 6 is an exemplary flowchart showing steps of manufacturing a rolled copper foil according to the present invention.

At first, is prepared an ingot (cast ingot) made of a tough pitch copper (e.g., JIS H3100 C1100), an oxygen-free copper (e.g., JIS H3100 C1020), or a copper alloy with the copper purity of 99.9% or more as a starting material (step a). Next, a hot rolling step in which the cast ingot thus formed is hot-rolled (step b) is carried out. After the hot rolling step, a cold rolling step in which the hot-rolled plate thus formed is cold-rolled (step c) and a process annealing step in which work hardening by the cold rolling is relaxed (step d) are conducted; steps c and d are properly repeated to produce a copper strip referred to as a green sheet. Then, an annealing step for green sheet (step d′), which is the process annealing step just before the final cold rolling step, is carried out. In the annealing step for green sheet, it is desirable that the previous working strain be sufficiently relaxed (e.g., almost full annealing be carried out).

After that, the final cold rolling step (step e, also sometimes referred to as a finish rolling step) is applied to the annealed green sheet to produce a rolled copper foil with a predetermined thickness. Surface treatment or the like is applied to the rolled copper foil after the final cold rolling step as necessary (step f); and the treated rolled copper foil is supplied to an FPC board manufacturing step (step g). As mentioned before, the recrystallization annealing is often carried out during the step g (e.g., the CCL step). In the present invention, the final cold rolling step means “step e” and the recrystallization annealing means an annealing step conducted after the final cold rolling step of “step e”.

In one manufacturing method of the rolled copper foil according to the present invention, one or more rolling passes in a second rolling pass and later in the final cold rolling step have a working ratio at least 1.1 times greater than an immediately preceding rolling pass. Accordingly, more rolled textures with {220}_(Cu) plane alignment are formed in the final stage of the final cold rolling step, and crystal grains with a cubic texture as a seed crystal can be positively formed in the rolled texture. It can then be considered that the seed crystals with the cubic texture contribute to a high degree of crystal grains orientation of the cubic texture due to the recrystallization annealing (details will be described later).

Preferably, one or more rolling passes in a second rolling pass and later in the final cold rolling step have a working ratio at least 1.15 times greater than an immediately preceding rolling pass. More preferably, one or more rolling passes in a second rolling pass and later in the final cold rolling step have a working ratio at least 1.2 times greater than an immediately preceding rolling pass. If a rolling pass has a working ratio that is smaller than the 1.1 times greater working ratio, it is difficult to form seed crystal grains of the cubic texture in the rolled texture.

Preferably, the final pass or the pass immediately before the final pass in the final cold rolling step has the largest working ratio per rolling pass through the second rolling pass and later (except the first rolling pass). This prevents the seed crystal grains with the cubic texture formed in the rolled texture from being rotated in another orientation as the rolling step proceeds (details will be described later). When the total working ratio in the final cold rolling step falls within a range from 80% or more to less than 90%, not only the total number of passes in the rolling step can be reduced but also it can be avoided that rolling control becomes difficult due to excessive work hardening, reducing the manufacturing cost. The manufacturing method in the present invention, which has features as described above, enables a rolled copper foil to have an improved flexible fatigue property and also enables the manufacturing cost to be reduced.

In another manufacturing method of the rolled copper foil according to the present invention, which substitutes for the above manufacturing method, the annealed green sheet is adjusted as described below at least by controlling the annealing step for green sheet (step d′). For a rolled copper foil (annealed copper foil) after the annealing step for green sheet (step d′) and before the final cold rolling step (step e), when the normalized intensity of the {220}_(Cu) plane diffractions of the copper crystal in results obtained by XRD pole figure measurement with respect to the rolled surface by the β axis scanning at respective α angles are plotted on the vertical axis with the α angle on the horizontal axis, the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°; the minimum value S of the normalized intensity appears in the range of the α angle from 20° to 40°; and the maximum value Q and the minimum value S have a relation of “2≦Q/S≦3”, this type of rolled copper foil being used as an annealed green sheet for the final cold rolling step. Furthermore, the final cold rolling step (step e) is applied to the annealed green sheet so that the total working ratio in the final cold rolling step falls within the range from 80% or more to less than 93%. When the green sheet is annealed, it is preferably held within a temperature range of 600° C. or higher to lower than 700° C. (actual temperatures of the copper foil, not setting temperature of a furnace) for 1 to 30 minutes. A more preferable temperature range is from 650° C. or higher to lower than 700° C.

Accordingly, the rolled copper foil of the present invention, which is characterized as follows, is obtained; in results obtained by the XRD pole figure measurement with respect to the rolled surface of the rolled copper foil after the final cold rolling step (step e) and before the recrystallization annealing, there is at least one group of crystal grains which exhibits four-fold symmetry, in which at least four peaks of the {220}_(Cu) plane diffraction of the copper crystal due to the one group of crystal grains exhibiting the four-fold symmetry, which is obtained by the β axis scanning with the α angle set to 450, appear at intervals of 90°±5° along the β angle; in addition, when the normalized intensity of the {220}_(Cu) plane diffractions of the copper crystal in results obtained by the XRD pole figure measurement with respect to the rolled surface by the β axis scanning at respective α angles are plotted on the vertical axis with the α angle on the horizontal axis, the maximum value P of the normalized intensity appears in the range of the α angle from 25° to 35°; the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°; the normalized intensity increases monotonically in the range of the α angle from 85° to 90°; and the maximum value P, the maximum value Q, and the normalized intensity R at the α angle of 90° have a relation of “Q≦P≦R”.

As described before, the {220}_(Cu) plane and {200}_(Cu) plane of the copper crystal geometrically form 45° (the angle formed between both planes is 45°). Therefore, it can be considered that the maximum value Q of the normalized intensity, which is present within the range of the α angle from 40° to 50°, is related to the degree of in-plane alignment of the {200}_(Cu) plane at the rolled surface of the rolled copper foil. In other words, the present invention features that crystal grains with both out-of-plane alignment and in-plane alignment of the {200}_(Cu) plane which are originally present at the rolled surface of the annealed green sheet remain to the extent that the relation of “Q≦P≦R” holds after the final cold rolling step (step e) is completed.

When the total working ratio in the final cold rolling step falls within the range from 80% or more to less than 93%, not only the total number of passes in the rolling step can be made smaller than conventional rolled copper foils with a high working ratio (e.g., 93% or more), but also it can be avoided that rolling control becomes difficult due to excessive work hardening, reducing a load applied to the manufacturing facility and the manufacturing cost. The manufacturing method according to the present invention, which has features as described above, enables a rolled copper foil to have an improved flexible fatigue property and also enables the manufacturing cost to be reduced.

(Discussion on Mechanism for Improving Flexible Fatigue Property)

Next, a mechanism for improving the flexible fatigue property of the rolled copper foil in an embodiment according to the present invention is described below.

When stress is applied to a metal crystal, dislocation in the crystal is likely to move along the slip plane of the crystal. However, a crystal grain boundary generally plays a barrier to the movement of the dislocation. In a polycrystalline rolled copper foil, when the dislocation concentrates on the grain boundary or the like due to bending motion, it can be considered that a crack is prone to occur at the concentrating portion and thereby so-called metal fatigue occurs. In other words, it is expected that the flexible fatigue property can be improved if the concentration of the dislocation is suppressed in the metal polycrystalline body.

The rolled copper foil in the preferred embodiments of the present invention strongly suggests that when crystal grain orientation of the rolled copper foil after the annealing step for green sheet and/or the final cold rolling step is controlled, the cubic texture after the recrystallization annealing can be controlled. It can be considered that when recrystallization occurs and thus a cubic texture for which the alignment of a {111}_(Cu) plane, which is a slip plane specific to the face-centered cubic structure of the copper crystal, is well controlled across the grain boundary is obtained (i.e., slip directions are well aligned), the possibility that the dislocation causes cross slip during the bending motion increases and thereby the flexible fatigue property is improved. That is, a way to form the cubic texture in which copper crystal grains are three-dimensionally oriented (the overall orientation ratio is high) is important.

When stress is applied to an object during rolling, it can be divided into a tensile stress component and a compressive stress component for the object. In cold rolling for a copper foil, the copper crystal in the copper foil rotates due to the stress caused during rolling and forms a rolled texture as the rolling proceeds. Generally, in the case of the compressive stress, the rotational direction (direction of the orientation at the rolled surface) of the crystal with respect to the stress direction is the {220}_(Cu) plane; and in the case of the tensile stress, the rotational direction is the {311}_(Cu) plane or the {211}_(Cu) plane. It has been considered that when working strain accompanying the rotation is accumulated, the accumulated working strain becomes a driving force for forming the cubic texture during recrystallization.

In view of the above situation, to improve the {220}_(Cu) plane alignment (rolled texture) of a conventional rolled copper foil and to accumulate more working strain in it, the total working ratio in the final cold rolling step is set to a high value (93% or more, for example) to increase the compressive stress. As described before, when the cubic texture is concerned, attention has been focused only to increase the occupation ratio of the {200}_(Cu) plane at the rolled surface (one-dimensional orientation in a normal direction to the rolled surface) and there has been no special consideration about the three-dimensional orientation of crystal grains at the rolled surface. Attention has also been focused only on the total working ratio in the final cold rolling step and there has been no special consideration about the working ratio per rolling pass. However, since the material (copper foil) is hardened due to work hardening as rolling proceeds, it can be generally thought that the working ratio per pass is reduced as rolling proceeds.

This pass schedule in the conventional method arises a problem in which after crystal grains have been oriented to the {220}_(Cu) plane by a high working ratio pass (rolling pass having a high working ratio per pass), part of these crystal grains may start to rotate in the {311}_(Cu) plane orientation or {211}_(Cu) plane orientation. This may be because a rolling pass having a high working ratio per pass causes the compressive stress component to be dominant and a rolling pass having a low working ratio per pass causes the tensile stress component to be dominant.

In a pass schedule in one manufacturing method of the rolled copper foil according to the present invention, one or more rolling passes through a second rolling pass and later in the final cold rolling step have a working ratio at least 1.1 times greater than an immediately preceding rolling pass. In a specific exemplary arrangement, the second or later rolling pass having a highest working ratio per pass is executed in a later half of the rolling pass schedule. In another exemplary arrangement, the working ratio per pass gradually increases after the second pass. In these rolling methods, the arrangement of the pass schedule is opposite to that in the conventional method. It is found that when a rolling pass having a high working ratio per pass is executed in the second pass or later in the final cold rolling step (particularly, in the latter half of the rolling pass schedule), partial recrystallization occurs in way of the rolling and seed crystal grains with the cubic texture (crystal gains oriented to the {200}_(Cu) plane) are formed in the rolled texture. It can be considered that the seed crystal grains with the cubic texture contribute to the highly oriented growth of the cubic texture in recrystallization annealing.

On the other hand, another manufacturing method of the rolled copper foil according to the present invention features that the annealed green sheet to be supplied for the final cold rolling step (step e) is controlled so that crystal grains with the cubic texture (oriented to the {200}_(Cu) plane) are left in the rolled texture to an extent that the relation of “Q≦P≦R” holds during the final cold rolling step (step e) as a formation step for {220}_(Cu) plane orientation. It can be considered that because crystal grains having the cubic texture, which are dispersed and left in the rolled texture, in which working strain is accumulated, function as the seed crystal grains for forming the cubic texture in recrystallization annealing, the crystal grains contribute to highly oriented growth (particularly, three-dimensional orientation).

Furthermore, in the manufacturing method of the rolled copper foil, the total working ratio in the final cold rolling step is within the range from 80% or more to less than 93%, and the crystal grains with the cubic textures (crystal grains in which there is no crystal plane rotation) are left, so it can be considered that working strain accumulated in the copper foil is sufficiently smaller than that in a rolled copper foil (with a working ratio of 93% or more, for example) in the prior art. This results in a small driving force for an atomic rearrangement during the recrystallization annealing, suppressing recrystallized grains from growing (suppressing crystal grains from becoming large). The suppression of excessive grain growth of the recrystallized grains provides a solution to a dish down phenomenon, which is problematic in the FPC board manufacturing step in recent years. In the dish down phenomenon, when a copper foil is subject to half etching during the FPC board manufacturing step, etching is prone to be performed for each crystal grain, so crystal grains with large diameters are etched with higher priority, forming craters at the surface of the copper foil.

Other Embodiments

In the step a, there are no restrictions on the melting and casting methods and also on the size of the starting materials. Also, there are no particular restrictions on the step b, step c, and step d; usual methods and conditions may be employed. Further, the thickness of the rolled copper foil used for an FPC board is generally 50 μm or less. Accordingly, there are also no particular restrictions on the thickness of the rolled copper foil of the present invention if it is 50 μm or less, but a thickness of 20 μm or less is particularly preferable.

[Manufacturing of a Flexible Printed Circuit Board]

A flexible printed circuit board can be obtained by a conventional manufacturing method using the rolled copper foil of the embodiments described above. Further, the recrystallization annealing for the rolled copper foil may be a heat treatment carried out in the usual CCL step, or it may be conducted in a separated step.

Advantages of the Embodiments

The embodiments of the present invention have the following advantages:

(1) A rolled copper foil having a more excellent flexible fatigue property than usual can be obtained.

(2) A rolled copper foil having a more excellent flexible fatigue property than usual can be manufactured stably and efficiently (i.e., at a low cost).

(3) Flexible wirings such as for flexible printed circuit (FPC) boards having a more excellent flexible fatigue property than usual can be obtained.

(4) The rolled copper foil can be applied not only to FPC boards but also to other conductive members requiring an improved flexible fatigue property (flexible fatigue life) such as a negative pole material of a vehicle-mounted lithium ion battery that needs to have endurance to vibration.

The present invention is described below in further details by using examples. However, the present invention is not limited to these examples described herein.

EXAMPLES Examples 1 to 5 and Comparative Examples 1 to 3

(Manufacturing Procedure)

First, tough pitch copper (with an oxygen content of 150 ppm) was prepared as a raw material, from which a cast ingot with a thickness of 200 mm and a width of 650 mm was then prepared. In accordance with the flowchart shown in FIG. 6, the cast ingot was hot-rolled down to a thickness of 10 mm. Then, cold rolling and process annealing (including annealing for green sheet) were properly repeated to prepare the annealed green sheets with the thicknesses of 0.1 mm and 0.2 mm. In the annealing step for green sheet, the green sheets were held at a temperature of about 700° C. for about one minute (Example 1 and Comparative example 1), held at a temperature of about 650° C. for about two minutes (Examples 2 and 4), held at a temperature of about 690° C. for about one minute (Examples 3 and 5), held at a temperature of about 550° C. for about two minutes (Comparative example 2), and held at a temperature of about 800° C. for about one minute (Comparative example 3). The temperature in annealing step for green sheet is the actual temperature of the copper foil rather than the temperature setting of the annealing furnace.

The final cold annealing step was executed for the above annealed green sheets under the conditions shown in Table 1 or 2 to prepare rolled copper foils with a thickness of 16 μm (Examples 1 to 5 and Comparative examples 1 to 3). Besides, there was a difference of a rolling speed (feeding rate) in the final cold rolling step between a group of Examples 2-3 and Comparative examples 2-3 and another group of Examples 4-5. Specifically, the rolling speed (feeding rate) in the final cold rolling step for the another group of Examples 4-5 was smaller than that for the group of Examples 2-3 and Comparative examples 2-3.

TABLE 1 Conditions in final cold annealing step Green sheet Working ratio per Total working thickness rolling pass ratio Example 1 0.1 mm 1st and 2nd passes: About 84% about 30% 3rd pass: about 40% 4th pass: about 46% Comparative 1st and 2nd passes: example 1 about 30% 3rd pass: about 20% 4th to 7th passes: about 15% 8th path: about 12% 9th path: about 11%

TABLE 2 Conditions in final cold annealing step Green sheet Working ratio per Total working thickness rolling pass ratio Example 2 0.2 mm 1st pass: about 40% About 92% Example 4 2nd pass: about 30% Comparative 3rd pass: about 25% example 2 4th pass to pass Example 3 0.1 mm immediately before last About 84% Example 5 pass: about 15% to 10% Comparative Last pass: about 10% example 3

(XRD Measurement for Rolled Copper Foils)

The XRD measurements were carried out for the rolled copper foils after the annealing step for green sheet, during the final cold rolling step, after the final cold rolling step, and after the recrystallization annealing, as described below. In various XRD measurements (2θ/θ measurement, rocking curve measurement, pole figure measurement, and in-plane alignment measurement), an X-ray diffraction apparatus RAD-B (manufactured by Rigaku Corps) was used. The Cu was used as an anticathode (target), and a tube voltage and a tube current were set to 40 kV and 30 mA, respectively. The size of a specimen served for the XRD measurements was about 15 mm×about 15 mm.

The XRD 2θ/θ measurement was conducted by using a general wide-angle goniometer within the range of 2θ from 40° to 100°. The slit conditions in the 2θ/θ measurement were a divergence slit of 10, a receiving slit of 0.15 mm, and a scatter slit of 10. In the XRD rocking curve measurement, the detector was fixed to a 2θ value of the {200}_(Cu) plane diffraction peak obtained by the 2θ/θ measurement, and a specimen was scanned within the range of θ from 15° to 35°. The slit conditions in the rocking curve measurement was the same as those in the 2θ/θ measurement.

In the XRD pole figure measurement and in-plane alignment measurement, the {220}_(Cu) plane diffraction intensity was measured by using a general Schulz reflection method in which the β angle was scanned from 0° to 360° (through in-plane rotation) within the range of the α angle of 15° to 90° (α is 90° when it is perpendicular to the rolled surface). 2θ was set to about 74° based on results obtained by preliminary measurement carried out for each specimen. As slit conditions, the divergence slit was set to 1°; the scatter slit was set to 7 mm; the receiving slit was set to 7 mm; and the Schulz slit (with a slit height of 1 mm) was used. In the in-plane alignment measurement, the α angle value was fixed to 45°.

Example 1 and Comparative Example 1

(Rolled Copper Foils after Final Cold Rolling Step)

The XRD in-plane alignment measurement was conducted for rolled copper foils with the thickness of 16 μm in Example 1 and Comparative example 1, to which rolling had been applied (after the final cold rolling step and before recrystallization annealing). FIG. 7A is an example of a diffraction pattern of XRD in-plane alignment measurement (measurement for the {220}_(Cu) plane with α set to 45°) carried out for the rolled copper foil immediately after the final cold rolling step in Example 1. FIG. 7B is another example of this measurement in Comparative example 1.

As seen from FIG. 7A, the rolled copper foil in Example 1 exhibited four-fold symmetric diffraction peaks at intervals of 90°±5°, as indicated by black arrows. The intensity of each of the four-fold symmetric diffraction peaks was at least 1.5 times stronger than the minimum intensity of the {220}_(Cu) plane diffraction obtained by the β axis scanning. This means that the {200}_(Cu) plane has superior in-plane alignment at the rolled surface of the copper foil. By comparison, as seen from FIG. 7B, although the rolled copper foil in Comparative example 1 exhibited weak diffraction peaks at β angles of about 0° (360°) and 180°, exhibited almost no diffraction peaks at β angles of about 90° and 270°.

FIG. 8 is an example of a diffraction pattern by XRD 2θ/θ measurement carried out for the rolled copper foil immediately after the final cold rolling step in Comparative example 1. FIG. 3 is an example of a diffraction pattern by XRD 2θ/θ measurement in Example 1. As described above, the rolled copper foil in Example 1, shown in FIG. 3, had many crystal grains oriented to the {200}_(Cu) plane at the rolled surface. Assuming diffraction peak intensity “I_({200}Cu)” on the {200}_(Cu) plane in FIG. 3 to be 100, diffraction peak intensity “I_({220}Cu)” on the {220}_(Cu) plane was 48. Considering that the ratio of the X-ray diffraction peak intensity on the {200}_(Cu) of copper crystal powder to that on the {220}_(Cu) plane is about “2:1”, it can be thought that crystal grains oriented to the {200}_(Cu) plane and crystal grains oriented to the {220}_(Cu) plane were present by approximately the same amount, in terms of their areas, at the rolled surface of the rolled copper foil in FIG. 3.

Assuming the diffraction peak intensity “I_({220}Cu)” on the {220}_(Cu) plane of the rolled copper foil in Comparative example 1 in FIG. 8 to be 100, the diffraction peak intensity “I_({200}Cu)” on the {200}_(Cu) plane was 76, indicating that crystal grains oriented to the {220}_(Cu) plane were overwhelmingly dominant at the rolled surface of the copper foil. This means that crystal grains oriented to the {200}_(Cu) plane, which became seed crystals, were very few.

The results in the above in-plane alignment measurement and 2θ/θ measurement show that three-dimensionally oriented copper crystals which could become seed crystal grains for forming cubic textures were certainly present in the rolled copper foil in Example 1. In contrast, for the rolled copper foil in Comparative example 1, it is indicated that although crystal grains oriented to the {200}_(Cu) plane with respect to the rolled surface were present, the crystal grains had poor in-plane alignment and there were almost no three-dimensionally oriented seed crystals.

Examples 2 to 5 and Comparative Examples 2 and 3 Annealed Green Sheets

The XRD pole figure measurement was conducted for Examples 2-5 and Comparative examples 2-3 of annealed green sheets (after the annealing step for green sheet and before the final cold rolling step) with thicknesses of 0.2 and 0.1 mm, which were prepared as described above. FIGS. 9A to 9D are examples of normalized intensity of {220}_(Cu) plane diffractions by the β axis scanning as a function of a angle by X-ray diffraction pole figure measurement, which was carried out for the rolled surfaces of the annealed green sheets in Example 2, Example 3, Comparative example 2, and Comparative example 3, respectively.

As seen from FIGS. 9A to 9D, all samples had the maximum value Q of the normalized intensity in the range of the α angle from 40° to 50° and the minimum value S of the normalized intensity in the range of the α angle from 20° to 40°. The ratio of the maximum value Q to the minimum value S (Q/S) was 2.2 in Example 2 and 2.6 in Example 3, falling in the range of 2 to 3. By comparison, the ratio was 3.1 in Comparative example 2 and 1.5 in Comparative example 3, falling out of this range. In Examples 4 and 5, similar results to Examples 2 and 3 on the normalized intensity of {220}_(Cu) plane diffractions and the ratio of the maximum value Q to the minimum value S (Q/S) were obtained, respectively.

(Rolled Copper Foils in Way of Final Cold Rolling Step)

The XRD pole figure measurement was conducted for rolled copper foils in way of the final cold rolling step which used the above four types of annealed green sheets. FIGS. 10A to 10D are examples of normalized intensity of {220}_(Cu) plane diffractions by the β axis scanning as a function of the α angle by XRD pole figure measurement, which was carried out for the rolled surfaces of the rolled copper foils in way of the final cold rolling step in Example 2, Example 3, Comparative example 2, and Comparative example 3, respectively.

As shown in FIGS. 10A to 10D, all samples had the maximum value P of the normalized intensity in the range of the α angle from 25° to 35° (or exhibit a tendency to have the maximum value P in that range) and the maximum value Q of the normalized intensity in the range of the α angle from 40° to 50°, and the normalized intensity increases monotonically in the range of the α angle from 85° to 90°. When compared with FIGS. 9A to 9D, it is also found that the maximum value Q of the normalized intensity was reduced. This reduction may be attributable to the copper crystal rotation, described above, which was caused by the stress during rolling.

(Rolled Copper Foils after Final Cold Rolling Step)

The XRD pole figure measurement was conducted for rolled copper foils with the thickness of 16 μm, to which rolling had been applied (after the final cold rolling step and before recrystallization annealing). FIGS. 11A to 11D are examples of normalized intensity of {220}_(Cu) plane diffractions by the β axis scanning as a function of the α angle by XRD pole figure measurement, which was carried out for the rolled surfaces of the rolled copper foils immediately after the final cold rolling step in Example 2, Example 3, Comparative example 2, and Comparative example 3, respectively.

As seen from FIGS. 11A to 11D, the rolled copper foils in Examples 2 and 3 had a relation of “Q≦P≦R”, but, for the rolled copper foil in Comparative example 2, P was smaller than Q and R was smaller than Q and, for the rolled copper foil in Comparative example 3, the maximum value Q was hardly detected. When the relationship of “Q≦P≦R” held, it can be considered that seed crystal grains with the in-plane aligned cubic textures were present by an appropriate amount and the rolled textures in which working strain was accumulated were present by a necessary amount. In contrast, Comparative example 3, in which the maximum value Q was hardly present, indicates that there were almost no in-plane aligned seed crystals. Comparative example 2, in which P was smaller than Q and R was smaller than Q, indicates that copper crystals with in-plane aligned textures might be present but rolled textures in which working strain was accumulated were not sufficiently formed. In Examples 4 and 5, similar results to Examples 2 and 3 on the relationship of “Q≦P≦R” were obtained, respectively.

FIGS. 12A to 12C are examples of a diffraction pattern by XRD 2θ/θ measurement on rolled copper foils immediately after the final cold rolling step in Example 2, Example 3, and Comparative example 2, respectively. FIGS. 12A and 12B respectively indicate that the rolled copper foils in Examples 2 and 3 included, at the rolled surface, many crystal grains oriented to the {200}_(Cu) plane. FIG. 11C indicates that although the rolled copper foil in Comparative example 2 included, at the rolled surface, many crystal grains oriented to the {200}_(Cu) plane, it also included many crystal grains oriented to the {111}_(Cu) plane and crystal grains oriented to the {220}_(Cu) plane were reduced. The result in Comparative example 3 was approximately the same as in FIG. 7; crystal grains oriented to the {200}_(Cu) plane, which became seed crystal grains, were few and crystal grains oriented to the {220}_(Cu) plane were dominant. In Examples 4 and 5, similar results to Examples 2 and 3 on the diffraction patterns were obtained, respectively.

FIG. 4 is an example of a pole figure by XRD pole figure measurement in Example 4 in a state after the final cold rolling step but before recrystallization annealing. As mentioned before, the four-fold symmetric diffraction peaks due to the another group of crystal grains (white-open arrows) according to the fourth embodiment were recognized within the range from 40° to 50° of the α angle in addition to those due to the one group of crystal grains (black arrows) according to the first embodiment. In Example 5, result of the pole figure similar to Example 4 was obtained while only three peaks among the four-fold symmetric diffraction peaks due to the another group of crystal grains were recognized (one diffraction peak was somewhat weak).

By contrast with Examples 4 and 5, in Examples 2 and 3 although the four-fold symmetric diffraction peaks due to the one group of crystal grains according to the first embodiment were confirmed within the range from 40° to 50° of the α angle, those due to the another group of crystal grains according to the fourth embodiment were not recognized. Furthermore, in Comparative examples 2 and 3, there were no four-fold symmetric diffraction peaks on the pole figures.

The results obtained by the above pole figure measurement and 2θ/θ measurement showed that three-dimensional-oriented copper crystals which could become seed crystal grains for forming cubic textures were present by an appropriate amount in the rolled copper foils in Examples 2 to 5. In contrast, for the rolled copper foil in Comparative example 3, it is indicated that although crystal grains oriented to the {200}_(Cu) plane with respect to the rolled surface were present, the crystal grains had poor in-plane alignment and there were almost no three-dimensional-oriented seed crystals. In Comparative example 2, crystal grains which had cubic textures and were oriented to the {200}_(Cu) plane were certainly present, but it can be considered that rolled textures in which working strain was accumulated were not sufficiently formed, the working strain being a driving force for forming cubic textures.

Examples 1 to 5 and Comparative Examples 1 to 3 Rolled Copper Foils after Recrystallization Annealing

Recrystallization annealing was carried out for rolled copper foils with the thickness of 16 μm after the final cold rolling step, which were prepared as described above; the rolled copper foils were held at 180° C. for 60 minutes. After that, the XRD measurements were carried out for the rolled copper foils. The overall orientation ratio “[A]×[B]×[C]” was then evaluated. Table 3 indicates results of the cubic texture ratio [A], Table 4 indicates results of out-of-plane alignment ratio [B] and the in-plane alignment ratio [C], and Table 5 indicates results of the overall orientation ratio “[A]×[B]×[C]”.

[A], [B], and [C] were calculated from the equations below, as described before.

Cubic texture ratio [A]=I _({220}Cu)/(I _({111}Cu) +I _({200}Cu) +I _({220}Cu) +I _({311}Cu))

Out-of-plane alignment ratio [B] of cubic texture=Δθ_(FWHM)/Δθ_(IW)

In-plane alignment ratio [C] of cubic texture=Δβ_(FWHM)/Δβ_(IW)

TABLE 3 Relative intensity when diffraction intensity of {200}_(Cu) plane is taken as 100, as well as values of [A] {111}_(Cu) {200}_(Cu) {220}_(Cu) {311}_(Cu) [A] Example 1 4 100 3 1 0.92 Example 2 2 100 3 1 0.94 Example 3 5 100 10 3 0.85 Example 4 3 100 3 1 0.94 Example 5 8 100 8 5 0.83 Comparative 5 100 5 4 0.88 example 1 Comparative 3 100 3 2 0.92 example 2 Comparative 10 100 35 9 0.65 example 3

TABLE 4 Values of out-of-plane alignment ratio [B] and in- plane alignment ratio [C] Δθ_(FWHM) Δθ_(IW) [B] Δβ_(FWHM) Δβ_(IW) [C] Example 1 6.8 7.9 0.86 6.5 8.0 0.81 Example 2 7.4 7.7 0.96 7.0 7.5 0.93 Example 3 6.9 8.0 0.86 6.5 7.9 0.82 Example 4 7.5 7.8 0.96 6.9 7.3 0.95 Example 5 6.9 7.9 0.87 7.2 8.2 0.88 Comparative 6.9 9.4 0.73 6.7 9.1 0.74 example 1 Comparative 6.9 9.6 0.72 6.5 9.2 0.71 example 2 Comparative 6.7 9.5 0.71 7.1 9.6 0.76 example 3

TABLE 5 Values of overall orientation ratio [A] × [B] × [C] [A] [B] [C] [A] × [B] × [C] Example 1 0.92 0.86 0.81 0.64 Example 2 0.94 0.96 0.93 0.84 Example 3 0.85 0.86 0.82 0.60 Example 4 0.94 0.96 0.95 0.86 Example 5 0.83 0.87 0.88 0.64 Comparative 0.88 0.73 0.74 0.48 example 1 Comparative 0.92 0.72 0.71 0.47 example 2 Comparative 0.65 0.71 0.76 0.35 example 3

As is clear from Table 5, the overall orientation ratio “[A]×[B]×[C]” of the rolled copper foils in Examples 1 to 5 is sufficiently larger than 0.5, but the ratio in Comparative examples 1 to 3 is smaller than 0.5. A possible explanation for this is that whether the ratio becomes larger 0.5 depends on the presence or absence of three-dimensional-oriented copper crystals, which become the seed crystal grains during cubic texture formation, and/or the extent that rolled textures in which the working strain is accumulated are formed.

(Flexible Fatigue Property of Rolled Copper Foils after Recrystallization Annealing)

The flexible fatigue property of the rolled copper foils with the thickness of 16 μm after recrystallization annealing, which were prepared as described above, in Examples 1 to 5 and Comparative examples 1 to 3 were evaluated as described below. FIG. 13 is a schematic illustration showing an outline of flexible fatigue property measurement (IPC-based fatigue test). A IPC-based sliding fatigue test apparatus SEK-31B2S from Shinetsu Engineering Co. was used to measure the flexible fatigue property under conditions that: R was 2.5 mm; an amplitude stroke was 10 mm; frequency was 25 Hz (the amplitude velocity was 1500 cycles/minute); a specimen width was 12.5 mm; a specimen length was 220 mm; and the longitudinal direction of a specimen was the rolling direction. Ten specimens were measured in each example. Measurement results are shown in Table 6.

TABLE 6 Results of IPC-based fatigue test for rolled copper foils after recrystallization annealing Number of cycles to failure (Cycles until rupture of bent portion) Average Maximum Minimum (10 specimens) value value Example 1 1.9 × 10⁶ 2.5 × 10⁶ 1.6 × 10⁶ Example 2 2.1 × 10⁶ 2.5 × 10⁶ 1.7 × 10⁶ Example 3 1.6 × 10⁶ 2.0 × 10⁶ 1.3 × 10⁶ Example 4 2.7 × 10⁶ 3.1 × 10⁶ 2.0 × 10⁶ Example 5 1.9 × 10⁶ 2.4 × 10⁶ 1.6 × 10⁶ Comparative 0.8 × 10⁶ 1.1 × 10⁶ 0.5 × 10⁶ example 1 Comparative 0.7 × 10⁶ 0.9 × 10⁶ 0.4 × 10⁶ example 2 Comparative 0.6 × 10⁶ 0.7 × 10⁶ 0.5 × 10⁶ example 3

As is clear from Table 6, the rolled foils in Examples 1 to 5 had a flexible fatigue life at least two times as long as those in Comparative examples 1 to 3 (the rolled copper foils in Examples 1 to 3 had a more improved flexible fatigue property). A possible factor for this longer flexible fatigue life is that the cubic textures of the rolled copper foils in Examples 1 to 5 had high overall orientation ratios (see Table 5).

Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth. 

1. A rolled copper foil obtained after a final cold rolling step but before recrystallization annealing, including a group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction pole figure measurement with respect to a rolled surface, wherein: at least four peaks of a {220}_(Cu) plane diffraction of a copper crystal due to the group of crystal grains exhibiting the four-fold symmetry, which is obtained by axis scanning with an α angle set to 45°, appear at intervals of 90°±5° along the β angle.
 2. The rolled copper foil according to claim 1, wherein: the diffraction peaks exhibiting the four-fold symmetry at intervals of 90°±5° along the β angle each have a diffraction intensity at least 1.5 times stronger than a minimum intensity of {220}_(Cu) plane diffractions of the copper crystal, which are obtained by the β axis scanning.
 3. The rolled copper foil according to claim 1, wherein: when normalized intensity of the {220}_(Cu) plane diffractions of the copper crystal in results obtained by the X-ray diffraction pole figure measurement with respect to the rolled surface by the β axis scanning at respective α angles are plotted on a vertical axis with the α angle on a horizontal axis, the maximum value P of the normalized intensity appears in the range of the α angle from 25° to 35°; the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°; the normalized intensity increases monotonically in the range of the α angle from 85° to 90°; and the maximum value P, the maximum value Q, and the normalized intensity R at an α angle of 90° have a relation of “Q≦P≦R”.
 4. The rolled copper foil according to claim 1, wherein: in results obtained by X-ray diffraction 2θ/θ measurement for the rolled surface, diffraction peak intensity of a {200}_(Cu) plane of the copper crystal is equal to or greater than that of the {220}_(Cu) plane of the copper crystal.
 5. The rolled copper foil according to claim 1, wherein: the rolled copper foil further includes another group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction pole figure measurement with respect to the rolled surface; and at intervals of 90°±10° of the β angle appear the {220}_(Cu) plane diffraction peaks due to the another group of crystal grains exhibiting the four-fold symmetry, which are obtained by the β axis scanning within the range of 40° to 50° of the α angle.
 6. A rolled copper foil obtained by applying a recrystallization annealing to the rolled copper foil according to claim 1, wherein: the rolled copper foil has a relation of “[A]×[B]×[C]≧0.5”, where [A] is a cubic texture ratio calculated from results by X-ray diffraction 2θ/θ measurement for the rolled surface, [B] is an out-of-plane alignment ratio calculated from results by X-ray diffraction rocking curve measurement for a crystal grain with the cubic texture, and [C] is an in-plane alignment ratio calculated from results by X-ray diffraction pole figure measurement for the crystal grain with respect to the rolled surface.
 7. A rolled copper foil to which a recrystallization annealing is applied after a final cold rolling step, wherein: the rolled copper foil has a relation of “[A]×[B]×[C]≧0.5”, where [A] is a cubic texture ratio calculated from results by X-ray diffraction 2θ/θ measurement for a rolled surface, [B] is an out-of-plane alignment ratio calculated from results by X-ray diffraction rocking curve measurement for a crystal grain with the cubic texture, and [C] is an in-plane alignment ratio calculated from results by X-ray diffraction pole figure measurement for the crystal grain with respect to the rolled surface.
 8. A manufacturing method of a rolled copper foil, wherein: the rolled copper foil obtained after a final cold rolling step but before recrystallization annealing includes a group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction pole figure measurement with respect to a rolled surface in which at least four peaks of a {220}_(Cu) plane diffraction of a copper crystal due to the group of crystal grains exhibiting the four-fold symmetry, which is obtained by β axis scanning with an α angle set to 45°, appear at intervals of 90°±5° along the β angle; and wherein: one or more rolling passes in a second rolling pass and later in the final cold rolling step have a working ratio at least 1.1 times greater than an immediately preceding rolling pass.
 9. The manufacturing method according to claim 7, wherein: a final pass or a pass immediately before the final pass in the final cold rolling step has the largest working ratio per pass through the second rolling pass and later.
 10. The manufacturing method according to claim 7, wherein: a total working ratio in the final cold rolling step is 80% or more and less than 90%.
 11. A manufacturing method of a rolled copper foil, wherein: the rolled copper foil obtained after a final cold rolling step but before recrystallization annealing includes a group of crystal grains which exhibits four-fold symmetry in results obtained by X-ray diffraction (XRD) pole figure measurement with respect to a rolled surface in which at least four peaks of a {220}_(Cu) plane diffraction of a copper crystal due to the group of crystal grains exhibiting the four-fold symmetry, which is obtained by β axis scanning with an α angle set to 45°, appear at intervals of 90°±5° along the β angle; wherein: when normalized intensity of the {220}_(Cu) plane diffractions of the copper crystal in results obtained by the XRD pole figure measurement with respect to the rolled surface by the β axis scanning at respective α angles are plotted on a vertical axis with the α angle on a horizontal axis, the maximum value P of the normalized intensity appears in the range of the α angle from 25° to 35°, the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°, the normalized intensity increases monotonically in the range of the α angle from 85° to 90°, and the maximum value P, the maximum value Q, and the normalized intensity R at the α angle of 90° have a relation of “Q≦P≦R”; wherein: when, in results obtained by the XRD pole figure measurement with β axis scanning at respective α angles with respect to the rolled surface of the rolled copper foil obtained after an annealing step for green sheet but before the final cold rolling step, the normalized intensity of the {220}_(Cu) plane diffractions of the copper crystal are plotted on the vertical axis with the α angle on the horizontal axis, the maximum value Q of the normalized intensity appears in the range of the α angle from 40° to 50°, the minimum value S of the normalized intensity appears in the range of the α angle from 20° to 40°, and the maximum value Q and the minimum value S have a relation of “2≦Q/S≦3”, this type of rolled copper foil being used as an annealed green sheet; and wherein: a total working ratio in the final cold rolling step is 80% or more and less than 93%. 